Some of the crude oils that oil companies have the occasion to pipeline contain "high" amounts (10 percent or more) of paraffin or wax. The wax will crystallize and accumulate as the temperature of the crude oil mass is lowered, thus increasing the viscosity of the crude oil and making it more difficult to pump at a given rate. In addition, if the flow of crude oil is stopped for a period of time greater than approximately 12 hours, the wax crystals will form an interconnected network which will impede flow when it comes time to restart the pipeline.
The force required to break the gel and begin flow is known as the gel strength. In some cases, the gel strength may be sufficiently high as to keep the flow from restarting. In the case of a subsea pipeline, the consequences could be disastrous. Presently, offshore platforms and terminal are designed to inject compounds known as pour-point depressants or wax crystal modifiers. These compounds serve to inhibit the interconnection of the wax crystals keeping the gel strength below the force needed to initiate flow of the pipeline. In many instances the cost of the treatment package is a major fraction of the cost of production.
The wax crystal modifiers used in waxy crude oils are solid materials which are marginally soluble in hydrocarbon fractions, particularly crude oils. They are more soluble in lighter hydrocarbon fractions, but even then may constitute only a small percentage of the modifier-solvent mix. Customarily the wax modifiers are dissolved in a light hydrocarbon fraction and are then stored for use as needed. In the case of an offshore platform, the extra volume and weight of solvent-chemical mixture requires expensive storage space which must be designed into the platform. Also, the substantial amount of solvent hydrocarbon fraction required increases processing cost in the refinery where this material is recovered from the crude oil. It would be advantageous to provide a process which would reduce the amount of wax modifier required and accordingly the cost and storage space required on the platform, as well as the refinery processing cost involved.
Ultrasonic processors are used to provide vibrational energy at very high frequencies (20,000-800,000 cycles per second). In a liquid medium, these oscillations create high shear strains which create microscopic gas pockets. These gas pockets, by collapsing and expanding, serve to enhance the shear strain to the point that weak molecular binding forces can be disrupted. For instance, biological tissues can be completely disrupted and homogenized by the application of ultrasonic energy. Ultrasonic energy has also found use in the depolymerization and viscosity control of synthetic and natural polymers. High-frequency vibration also has been utilized to enhance chemical reactions.